Engine control device

ABSTRACT

Provided is a control device for an engine comprising an engine whose combustion mode is switchable according to an engine operation state, wherein the control device is capable of controlling the engine while suppressing generation of knock noise due to abnormal combustion. The control device comprises: a basic target torque-determining part (61) configured to determine a basic target torque based on a vehicle driving state including manipulation of an accelerator pedal; a torque reduction amount-determining part (63) configured to determine a torque reduction amount based on a vehicle driving state other than the manipulation of the accelerator pedal; a final target torque-determining part (65) configured to determine a final target torque based on the basic target torque and the torque reduction amount; and an engine control part (69) configured to set the combustion mode to a premixed combustion mode or a diffusion combustion mode according to the engine operation state. The engine control part is configured, when the engine operation state changes from a diffusion combustion region to a premixed combustion region, due to a change in the final target torque corresponding to a change in the torque reduction amount, to maintain the combustion mode in the diffusion combustion mode.

TECHNICAL FIELD

The present invention relates to an engine control device, and moreparticularly to a control device for an engine (internal combustionengine) whose combustion mode is switchable according to an engineoperation state.

BACKGROUND ART

Heretofore, there has been known a control device capable of, in asituation where the behavior of a vehicle becomes unstable due to roadwheel slip or the like, controlling the vehicle behavior to enable asafe traveling (e.g., an antiskid brake device). Specifically, there hasbeen known a control device operable to detect the occurrence of vehicleundersteer or oversteer behavior during vehicle cornering or the like,and apply an appropriate degree of deceleration to one or more roadwheels so as to suppress such behavior.

There has also been known a vehicle motion control device operable toadjust a degree of deceleration during vehicle cornering to therebyadjust a load to be applied to front road wheels as steerable roadwheels so as to enable a series of manipulations (braking, turning of asteering wheel, accelerating, turning-back of the steering wheel, etc.)by a driver during vehicle cornering under a normal traveling conditionto be performed naturally and stably, differently from theaforementioned control for improving safety in a traveling conditioncausing the vehicle behavior to become unstable (see, for example, thefollowing Patent Document 1).

Further, there has been proposed a vehicle behavior control deviceoperable to reduce a vehicle driving force according to a yawrate-related quantity (e.g., yaw acceleration) corresponding to steeringwheel manipulation by a driver, thereby making it possible to quicklygenerate vehicle deceleration in response to start of the steering wheelmanipulation by the driver and thus quickly apply a sufficient load tofront road wheels as steerable road wheels (see, for example, thefollowing Patent Document 2). In this vehicle behavior control device,in response to start of the steering wheel manipulation, a load isquickly applied to the front road wheels to cause an increase infrictional force between each of the front road wheels and a roadsurface and thus an increase in cornering force of the front roadwheels, thereby providing an improved turn-in ability of a vehicle in aninitial phase after entering a curve, and an improved responsivity withrespect to turning manipulation of a steering wheel. This makes itpossible to realize vehicle behavior just as intended by the driver.

CITATION LIST [Patent Document]

Patent Document 1: JP 2011-88576A

Patent Document 2: JP 2014-166014A

SUMMARY OF INVENTION Technical Problem

In the field of internal combustion engines such as a gasoline engineand a diesel engine, there has been known one type of engine whosecombustion mode is switchable according to an engine operation state.For example, in the field of diesel engines, there has been known onetype of diesel engine whose combustion mode is switchable between adiffusion combustion mode in which fuel is combusted while beinginjected into a cylinder, and a premixed combustion mode in which fuelis ignited after being preliminarily mixed with air in a cylinder.

Assume that, in a control device for such an engine, a current targettorque is instantaneously reduced by the vehicle behavior control devicedescribed in the Patent Document 2, so as to generate vehicledeceleration according to manipulation of a steering wheel by a driver.In this case, the combustion mode of the engine can be switched from thediffusion combustion mode to the premixed combustion mode, in responseto the change in the target torque. During the diffusion combustion inwhich fuel is combusted while being injected into a cylinder, with aview to suppressing degradation of emission quality due to incompletecombustion, an oxygen concentration in a cylinder (in-cylinder oxygenconcentration) is set to a relatively high value, as compared to duringthe premixed combustion. Thus, when the combustion mode is switched fromthe diffusion combustion to the premixed combustion, the in-cylinderoxygen concentration needs to be reduced.

Specifically, when a fuel injection amount is reduced so as toinstantaneously reduce the target torque, the in-cylinder oxygenconcentration needs to be reduced according to the reduction in the fuelinjection amount. However, control of the in-cylinder oxygenconcentration cannot catch up with the reduction in the fuel injectionamount, causing a relative increase in the in-cylinder oxygenconcentration. As a result, an actual in-cylinder oxygen concentrationbecomes higher than a suitable in-cylinder oxygen concentration for thepremixed combustion, and resulting abnormal combustion such as prematureignition undesirably causes generation of knock noise.

The present invention has been made to solve the above conventionalproblem, and an object thereof is to provide a control device for anengine whose combustion mode is switchable according to an engineoperation state, wherein the control device is capable of controllingthe engine to accurately realize vehicle behavior intended by a driver,while suppressing generation of knock noise due to abnormal combustion.

Solution to Technical Problem

In order to achieve the above object, the present invention provides acontrol device for an engine comprising an engine whose combustion modeis switchable according to an engine operation state. The engine controldevice comprises: a basic target torque-determining part configured todetermine a basic target torque based on a driving state of a vehicleincluding manipulation of an accelerator pedal; a torque reductionamount-determining part configured to determine a torque reductionamount based on a driving state of the vehicle other than themanipulation of the accelerator pedal; a final target torque-determiningpart configured to determine a final target torque based on the basictarget torque and the torque reduction amount; and an engine controlpart configured to control the engine to output the final target torque,wherein the engine control part configured, when the engine operationstate is in a predetermined premixed combustion region, to set thecombustion mode of the engine to a premixed combustion mode, and, whenthe engine operation state is in a predetermined diffusion combustionregion, to set the combustion mode of the engine to a diffusioncombustion mode, and wherein the engine control part is configured, whenthe engine operation state changes from the diffusion combustion regionto the premixed combustion region, due to a change in the final targettorque corresponding to a change in the torque reduction amount, tomaintain the combustion mode of the engine in the diffusion combustionmode.

In the control device of the present invention having the above feature,the engine control part is configured to control the engine to outputthe final target torque reflecting the torque reduction amountdetermined based on the vehicle driving state other than themanipulation of the acceleration pedal, so that it is possible tocontrol the engine to obtain the torque reduction amount with highresponsivity with respect to the vehicle driving state other than themanipulation of the accelerator pedal, to thereby quickly apply a loadto front road wheels. This makes it possible to control the engine toaccurately realize vehicle behavior intended by a driver.

Further, the engine control part is configured, when the engineoperation state changes from the diffusion combustion region to thepremixed combustion region, due to a change in the final target torquecorresponding to a change in the torque reduction amount, to maintainthe combustion mode of the engine in the diffusion combustion mode, sothat it is possible to avoid the need to reduce an in-cylinder oxygenconcentration in response to switching of the combustion mode from thediffusion combustion mode to the premixed combustion mode, and thussuppress an increase in difference between an actual in-cylinder oxygenconcentration and a suitable in-cylinder oxygen concentration for thecombustion mode. This makes it possible to suppress generation of knocknoise due to abnormal combustion such as premature ignition.

Preferably, in the control device of the present invention, the torquereduction amount-determining part is configured to determine the torquereduction amount according to manipulation of a steering wheel of thevehicle.

According to this feature, a temporal change in the torque reductionamount determined based on the manipulation of the steering wheel can bereflected on a temporal change in the final target torque, so that it ispossible to quickly add, to the vehicle, deceleration according to themanipulation of the steering wheel by a driver to thereby apply a loadto front road wheels to quickly increase a cornering force, therebyimproving responsivity with respect to the manipulation of the steeringwheel. This makes it possible to control the engine to accuratelyrealize vehicle behavior intended by the driver, while suppressinggeneration of knock noise due to abnormal combustion such as prematureignition.

Preferably, in the control device of the present invention, the enginecontrol part is configured, when the engine operation state changes fromthe premixed combustion region to the diffusion combustion region, dueto a change in the final target torque corresponding to a change in thetorque reduction amount, to switch the combustion mode of the enginefrom the premixed combustion mode to the diffusion combustion mode.

According to this feature, when the in-cylinder oxygen concentrationrises according to a reduction in the final target torque correspondingto a change in the torque reduction amount, the suitable in-cylinderoxygen concentration for the combustion mode also rises in response tothe switching of the combustion mode from the premixed combustion modeto the diffusion combustion mode, so that it is possible to suppress anincrease in difference between an actual in-cylinder oxygenconcentration and the suitable in-cylinder oxygen concentration for thecombustion mode, and thus appropriately set the combustion modeaccording to the engine operation state, while suppressing generation ofknock noise due to abnormal combustion such as premature ignition. Thismakes it possible to achieve enhanced combustion stability and improvedemission quality.

In the control device of the present invention, when the engine is adiesel engine comprising a fuel injector for injecting fuel into acylinder, the engine control part is preferably configured to controlthe fuel injector to regulate a fuel injection amount so as to enablethe diesel engine to output the final target torque.

According to this feature, by changing the fuel injection amount of thediesel engine according to a final target torque reflecting the torquereduction amount, it becomes possible to accurately realize a temporalchange in the torque reduction amount determined based on the vehicledriving state other than the manipulation of the accelerator pedal, withhigh responsivity. This makes it possible to control the diesel engineto accurately realize vehicle behavior intended by a driver.

Effect of Invention

The control device of the present invention can control the engine whosecombustion mode is switchable according to an engine operation state, soas to accurately realize vehicle behavior intended by a driver, whilesuppressing generation of knock noise due to abnormal combustion.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram depicting a configuration of an enginesystem employing an engine control device according to one embodiment ofthe present invention.

FIG. 2 is a block diagram depicting an electrical configuration of theengine control device according to this embodiment.

FIG. 3 is a flowchart of an engine control processing routine to beexecuted by the engine control device according to this embodiment, soas to control the engine.

FIG. 4 is a flowchart of a torque reduction amount determinationprocessing subroutine to be executed by the engine control deviceaccording to this embodiment, so as to determine a torque reductionamount.

FIG. 5 is a map presenting a relationship between steering speed, andtarget additional deceleration to be determined by the engine controldevice according to this embodiment.

FIG. 6 is a flowchart of a combustion mode determination processingsubroutine to be executed by the engine control device according to thisembodiment, so as to determine a combustion mode.

FIG. 7 is a map conceptually presenting engine operation regions to beused by the engine control device according to this embodiment, ascriteria for switching between combustion modes.

FIG. 8 is a map presenting a relationship of a difference between anestimated in-cylinder oxygen concentration and a target in-cylinderoxygen concentration, and a fuel injection parameter correction value.

FIG. 9 presents a temporal change in each parameter regarding enginecontrol to be performed by the engine control device according to thisembodiment during turning of a vehicle equipped with this engine controldevice, wherein: chart (a) is a top plan view schematically depictingthe vehicle which is turning in a clockwise direction; chart (b) is atime chart presenting a change in steering angle of the vehicle which isturning in the clockwise direction as depicted in chart (a); chart (c) atime chart presenting a change in steering speed of the vehicle which isturning in the clockwise direction as depicted in chart (a); chart (d)is a time chart presenting a change in additional decelerationdetermined based on the steering speed presented in chart (c); chart (e)is a time chart presenting a change in torque reduction amountdetermined based on the additional deceleration presented in chart (d);chart (f) is a time chart presenting changes in basic target torquebefore and after being smoothed by a torque variation filter; chart (g)is a time chart presenting a change in fuel injection-controlling finaltarget torque determined based on the basic target torque and the torquereduction amount; chart (h) is a time chart presenting a change in EGRand turbocharger-controlling final target torque determined based on thebasic target torque; chart (i) is a time chart presenting a change inrequired fuel injection amount determined based on the fuelinjection-controlling final target torque; chart (j) is a time chartpresenting a change in target in-cylinder oxygen concentration and achange in actual in-cylinder oxygen concentration, in the case where afuel injection amount is controlled as presented in chart (i); chart (k)is a time chart presenting a change in the difference between an actualin-cylinder oxygen concentration and the target in-cylinder oxygenconcentration; and chart (1) is a time chart presenting a change in yawrate (actual yaw rate) generated in the vehicle when the control of thefuel injection amount is performed as presented in chart (i), and achange in actual yaw rate generated in the vehicle when the control ofthe fuel injection amount based on the torque reduction amountdetermined by a torque reduction amount-determining part is notperformed.

DESCRIPTION OF EMBODIMENTS

With reference to the accompanying drawings, an engine control device ofthe present invention will now be described based on an embodimentthereof.

<System Configuration>

First of all, an engine system employing an engine control deviceaccording to one embodiment of the present invention will be describedwith reference to FIG. 1. FIG. 1 is a schematic diagram depicting aconfiguration of the engine system employing the engine control deviceaccording to this embodiment.

As depicted in FIG. 1, the engine system 200 primarily comprises: anengine (internal combustion engine) E designed as a diesel engine; anintake system IN for supplying intake air to the engine E; a fuel supplysystem FS for supplying fuel to the engine E; an exhaust system EX fordischarging exhaust gas from the engine E; aftermentioned varioussensors 96 to 110 for detecting various states pertaining to the enginesystem 200; and a power-train control module (PCM) 60 for controllingthe engine system 200.

First, the intake system IN comprises an intake passage 1 for allowingintake air to pass therethrough. The intake passage 1 is provided with:an air cleaner 3 for cleaning intake air introduced from outside; acompressor constituting a turbocharger 5 and configured to compressintake air passing therethrough to cause a rise in intake pressure; anintercooler 8 for cooling intake air by external air or cooling water;an intake shutter valve 7 for regulating a flow volume of intake airpassing therethrough; and a surge tank 12 for temporarily storing intakeair to be supplied to the engine E, which are arranged in this orderfrom the side of an upstream end of the intake passage 1.

Further, in the intake system IN, the intake passage 1 is provided with:an airflow sensor 101 for detecting an intake air amount at a positionimmediately downstream of the air cleaner 3; an intake air temperaturesensor 102 for detecting an intake air temperature at the positionimmediately downstream of the air cleaner 3; an intake air pressuresensor 103 for detecting an intake air pressure inside the turbocharger5; and an intake air temperature sensor 106 for detecting the intake airtemperature at a position immediately downstream of the intercooler 8.Further, the intake shutter value 7 is provided with an intake shuttervalve position sensor 105 for detecting an opening degree of the intakeshutter valve 7, and the surge tank 12 is provided with an intake airpressure sensor 108 for detecting the intake air pressure in an intakemanifold. These various sensors 101 to 108 provided in the intake systemIN are operable to output, to the PCM 60, detection signals S101 to S108corresponding to respective ones of the detected parameter values.

Second, the engine E is provided with: an intake valve 15 forselectively introducing intake air supplied from the intake passage 1(specifically, the intake manifold) into a combustion chamber 17thereof; a fuel injector 20 for injecting fuel toward the combustionchamber 17; a piston 23 reciprocatingly movable according to combustionof an air-fuel mixture in the combustion chamber 17; a crankshaft 25configured to be rotated according to the reciprocating movement of thepiston 23; and an exhaust valve 27 for selectively discharging, to anaftermentioned exhaust passage 41, exhaust gas produced by thecombustion of the air-fuel mixture in the combustion chamber 17.

Third, the fuel supply system FS comprises a fuel tank 30 for storingfuel therein, and a fuel supply passage 38 for supplying the fuel fromthe fuel tank 30 to the fuel injector 20. The fuel supply passage 38 isprovided with a low-pressure fuel pump 31, a high-pressure fuel pump 33,and a fuel injection common rail 35, which are arranged in this orderfrom an upstream end of the fuel supply passage 38.

Fourth, the exhaust system EX comprises an exhaust passage 41 forallowing exhaust gas to pass therethrough. The exhaust passage 41 isprovided with: a turbine constituting the turbocharger 5 and configuredto be rotated by exhaust gas passing therethrough, so as to rotationallydrive the compressor in the aforementioned manner; and a dieseloxidation catalyst (DOC) 45 and a diesel particulate filter (DPF) 46having an exhaust gas purification function, which are arranged in thisorder from the side of an upstream end of the exhaust passage 41. TheDOC 45 is a catalyst capable of oxidizing hydrocarbon (HC) and carbonmonoxide (CO) by using oxygen contained in exhaust gas to therebyconvert them into water and carbon dioxide, and the DPF 46 is a filtercapable of capturing particulate matter (PM) contained in exhaust gas.

Further, in the exhaust system EX, the exhaust passage 41 is providedwith: an exhaust gas pressure sensor 109 for detecting an exhaust gaspressure at a position upstream of the turbine of the turbocharger 5;and a linear O₂ sensor 110 for detecting an oxygen concentration at aposition immediately downstream of the DPF 46. These sensors 109, 110provided in the exhaust system EX are operable to output, to the PCM 60,detection signals S109, S110 corresponding to respective ones of thedetected parameter values.

Further, in this embodiment, the turbocharger 5 is constructed as atwo-stage supercharging system capable of efficiently obtaining highsupercharging in the entire engine speed range from a low engine speedrange having relatively low exhaust energy to a high engine speed range.More specifically, the turbocharger 5 comprises: a large turbocharger 5a for supercharging a large amount of air in the high engine speedrange; and a small turbocharger 5 b capable of efficiently performingsupercharging even under relatively low exhaust energy; a compressorbypass valve 5 c for controlling a flow of intake air to a compressor ofthe small turbocharger 5 b; a regulator valve 5 d for controlling a flowof exhaust gas to a turbine of the small turbocharger 5 b; and a wastegate valve 5 e for controlling a flow of exhaust gas to a turbine of thelarge turbocharger 5 a. These valves are configured to be drivenaccording to an operation state of the engine E (engine speed and engineload), so as to switch among a plurality of supercharging modes usingthe large turbocharger 5 a and the small turbocharger 5 b.

The engine system 200 in this embodiment further comprises an EGR device43. The EGR device 43 comprises: an EGR passage 43 a connecting an areaof the exhaust passage 42 upstream of the turbine of the turbocharger 5to an area of the intake passage 1 downstream of the compressor of theturbocharger 5 (specifically, downstream of the intercooler 8); and anEGR valve 43 b for adjusting a flow volume of exhaust gas to be allowedto pass through the EGR passage 43 a.

An amount of exhaust gas to be recirculated to the intake system IN bythe EGR device 43 (hereinafter referred to as “EGR gas amount”) isroughly determined by the exhaust gas pressure at a position upstream ofthe turbine of the turbocharger 5, the intake air pressure produced bythe opening degree of the intake shutter valve 7, and an opening degreeof the EGR valve 43 b.

Next, with reference to FIG. 2, an electrical configuration of theengine control device according to this embodiment will be described.FIG. 2 is a block diagram depicting the electrical configuration of theengine control device according to this embodiment.

The PCM 60 (engine control device) according to this embodiment isoperable to output control signals S130 to S132 to perform respectivecontrols for turbocharger 5, the fuel injector 20 and the EGR device 43,based on detection signals S96 to S100 output, respectively, from: asteering angle sensor 96 for detecting a rotational angle of a steeringwheel of a vehicle mounting the engine system 200 (steering angle); anaccelerator position sensor 97 for detecting an angular position of anaccelerator pedal (accelerator position); a vehicle speed sensor 98 fordetecting a vehicle speed; an ambient temperature sensor 99 fordetecting an ambient temperature; and an atmospheric pressure sensor 100for detecting atmospheric pressure, in addition to the detection signalsS101 to S110 from the aforementioned various sensors 101 to 110.

The PCM 60 comprises: a basic target torque-determining part 61configured to determine a basic target torque based on a driving stateof the vehicle including manipulation of the accelerator pedal; a torquereduction amount-determining part 63 configured to determine a torquereduction amount based on a driving state of the vehicle other than themanipulation of the accelerator pedal; a final target torque-determiningpart 65 configured to determine a final target torque based on the basictarget torque and the torque reduction amount; a torque variation filter67 configured to smooth a temporal variation of the final target torque;and an engine control part 69 configured to control the engine E tooutput the final target torque.

The above parts of the PCM 60 are realized by a computer whichcomprises: a CPU; various programs (including a basic control programsuch as an OS, and an application program capable of being activated onthe OS to realize a specific function) to be interpreted and executed bythe CPU; and an internal memory such as ROM or RAM storing therein theprograms and a variety of data.

Next, with reference to FIGS. 3 to 8, processing to be performed by theengine control device will be described.

FIG. 3 is a flowchart of an engine control processing routine to beexecuted by the engine control device according to this embodiment, soas to control the engine E, and FIG. 4 is a flowchart of a torquereduction amount determination processing subroutine to be executed bythe engine control device according to this embodiment, so as todetermine the torque reduction amount. FIG. 5 is a map presenting arelationship between steering speed, and target additional decelerationto be determined by the engine control device according to thisembodiment. FIG. 6 is a flowchart of a combustion mode determinationprocessing subroutine to be executed by the engine control deviceaccording to this embodiment, so as to determine a combustion mode. FIG.7 is a map conceptually presenting engine operation regions to be usedby the engine control device according to this embodiment, as criteriafor switching between combustion modes. FIG. 8 is a map presenting arelationship of a difference between an estimated in-cylinder oxygenconcentration and a target in-cylinder oxygen concentration, and a fuelinjection parameter correction value.

The engine control processing routine in FIG. 3 is activated when anignition switch of the vehicle is turned on to apply power to the enginecontrol device, and repeatedly executed.

As depicted in FIG. 3, upon start of the engine control processingroutine, in step S1, the PCM 60 operates to acquire information about adriving state of the vehicle. Specifically, the PCM 60 operates toacquire, as the driving state, detection signals S96 to S110 and thelike output from the aforementioned various sensors 96 to 110, includingthe steering angle detected by the steering angle sensor 96, theaccelerator position detected by the accelerator position sensor 97, thevehicle speed detected by the vehicle speed sensor 98, and a gear stagecurrently set in a transmission of the vehicle.

Subsequently, in step S2, the basic target torque-determining part ofthe PCM 60 operates to set a target acceleration based on the drivingstate of the vehicle including the manipulation of the accelerator pedalacquired in the step S1. Specifically, the basic targettorque-determining part operates to select, from a plurality ofacceleration characteristic maps defined with respect to various vehiclespeeds and various transmission gear stages (the maps are created inadvance and stored in a memory or the like), one accelerationcharacteristic map corresponding to a current vehicle speed and acurrent transmission gear stage, and determine, as the targetacceleration, an acceleration corresponding to a current acceleratorposition, with reference to the selected acceleration characteristicmap.

Subsequently, in step S3, the basic target torque-determining section 61operates to determine the basic target torque of the engine E forrealizing the target acceleration determined in the step S2. In thiscase, the basic target torque-determining part 61 operates to determinethe basic target torque within a torque range which can be produced bythe engine E, based on current vehicle speed, transmission gear stage,road grade, road surface mu (μ), etc.

Subsequently, in step S4, the torque variation filter 67 operates tosmooth a temporal variation of the basic target torque determined in thestep S3. As a specific technique for the smoothing, it is possible toemploy various known techniques (e.g., a technique of limiting a changerate of the basic target torque to a threshold or less, and a techniqueof calculating a moving average of the temporal variation of the basictarget torque).

In parallel with the processings in the steps S2 and S4, in step S5, thetorque reduction amount-determining part 63 operates to perform a torquereduction amount determination processing subroutine for determining thetorque reduction amount based on the vehicle driving state other thanthe manipulation of the steering wheel. This torque reduction amountdetermination processing subroutine will be described with reference toFIG. 4.

As depicted in FIG. 4, upon start of the torque reduction amountdetermination processing subroutine, in step S21, the torque reductionamount-determining part 63 operates to determine whether or not anabsolute value of the steering angle acquired in the step S1 isincreasing. As a result, when the absolute value of the steering angleis increasing, the subroutine proceeds to step S22. In the step S22, thetorque reduction amount-determining part 63 operates to calculate asteering speed based on the steering angle acquired in the step S1.

Subsequently, in step S23, the torque reduction amount-determining part63 operates to determine whether or not an absolute value of thesteering speed is decreasing.

As a result, when the absolute value of the steering speed is notdecreasing, i.e., the absolute value of the steering speed is increasingor the absolute value of the steering speed does not change, thesubroutine proceeds to step S24. In the step S24, the torque reductionamount-determining part 63 operates to obtain a target additionaldeceleration based on the calculated steering speed. This targetadditional deceleration is a deceleration to be added to the vehicleaccording to the manipulation of the steering wheel, so as to accuratelyrealize vehicle behavior intended by a driver.

Specifically, the torque reduction amount-determining part 63 operatesto obtain a value of the target additional deceleration corresponding tothe steering speed calculated in the step S22, based on a relationshipbetween the target additional deceleration and the steering speed,indicated by the map in FIG. 5.

In FIG. 5, the horizontal axis represents the steering speed, and thevertical axis represents the target additional deceleration. As depictedin FIG. 5, when the steering speed is less than a threshold T_(S) (e.g.,10 deg/s), a corresponding value of the target additional decelerationis 0. That is, when the steering speed is less than the threshold T_(S),the control of adding deceleration to the vehicle according to themanipulation of the steering wheel is not performed.

On the other hand, when the steering speed is equal to or greater thanthe threshold T_(S), a value of the target additional decelerationcorresponding to this steering speed comes closer to a given upper limitvalue D_(max) (e.g., 1 m/s²). That is, as the steering speed becomeslarger, the target additional deceleration becomes larger, and anincrease rate of the target additional deceleration becomes smaller.

Subsequently, in the step S25, the torque reduction amount-determiningpart 63 operates to determine an additional deceleration in the currentprocessing cycle (current-cycle additional deceleration), under thecondition that the increase rate of the additional deceleration is equalto or less than a threshold R_(max) (e.g., 0.5 m/s³).

Specifically, the torque reduction amount-determining part 63 operatesto, when an increase rate from the additional deceleration determined inthe last processing cycle (last-cycle additional deceleration) to thetarget additional deceleration obtained in the step S24 in the currentcycle is equal to or less than the threshold R_(max), determine thetarget additional deceleration obtained in the step S24, as thecurrent-cycle additional deceleration.

On the other hand, the torque reduction amount-determining part 63operates to, when the increase rate from the last-cycle additionaldeceleration to the target deceleration obtained in the step S24 in thecurrent processing cycle is greater than the threshold R_(max),determine, as the current-cycle additional deceleration, a valueobtained by increasing the last-cycle additional deceleration at theincrease rate R_(max) for the given cycle period.

Referring to the step S23 again, when the absolute value of the steeringspeed is decreasing, the subroutine proceeds to step S26. In the stepS26, the torque reduction amount-determining part 63 operates todetermine the last-cycle additional deceleration as the current-cycleadditional deceleration. That is, when the absolute value of thesteering speed is decreasing, an additional deceleration correspondingto a maximum value of the steering speed (i.e., a maximum value of theadditional deceleration) is maintained.

Referring to the step S21 again, when the absolute value of the steeringangle is not increasing (i.e., is maintained constant or is decreasing),the subroutine proceeds to step S27. In the step S27, the torquereduction amount-determining part 63 operates to obtain an amount(deceleration reduction amount) by which the last-cycle additionaldeceleration is to be reduced in the current processing cycle. Forexample, the deceleration reduction amount may be calculated based on aconstant reduction rate (e.g., 0.3 m/s³) preliminarily stored in amemory or the like. Alternatively, the deceleration reduction amount maybe calculated based on a reduction rate determined according to thevehicle driving state acquired in the step S1 and/or the steering speedcalculated in Step S22.

Subsequently, in step S28, the torque reduction amount-determining part63 operates to determine the current-cycle additional deceleration bysubtracting the deceleration reduction amount obtained in the step S27from the last-cycle additional deceleration.

After completion of the step S25, S26 or S28, in step S29, the torquereduction amount-determining part 63 operates to determine the torquereduction amount, based on the current-cycle additional decelerationdetermined in the step S25, S26 or S28. Specifically, the torquereduction amount-determining part 63 operates to determine a value ofthe torque reduction amount required for realizing the current-cycleadditional deceleration, based on the current vehicle speed,transmission gear stage, road grade and others acquired in the Step S1.After completion of the step S29, the torque reductionamount-determining part 63 operates to terminate the torque reductionamount determination processing subroutine, and the subroutine returnsto the main routine.

Returning to FIG. 3 again, after completion of the processings in thesteps S2 to S4 and the torque reduction amount determination processingsubroutine in the step S5, in step S6, the engine control part 69operates to execute a combustion mode setting processing subroutine forsetting the combustion mode of the engine E according to the operationstate of the engine E. This combustion mode setting processingsubroutine will be described with reference to FIG. 6.

As depicted in FIG. 6, upon start of the combustion mode settingprocessing subroutine, in step S31, the engine control part 69 operatesto determine where or not there is a need for torque reduction based onthe vehicle driving state other than the manipulation of the acceleratorpedal. Specifically, when the torque reduction amount determined in thetorque reduction amount determination processing subroutine in the stepS5 is greater than 0, the engine control part 69 operates to determinethat there is the need for the torque reduction.

As a result, when there is the need for the torque reduction, thesubroutine proceeds to step S32. In the step S32, the final targettorque-determining part 65 operates to subtract the torque reductionamount determined in the torque reduction amount determinationprocessing subroutine in the step S5 from the basic target torque afterbeing smoothed in the step S4, to thereby determine a fuelinjection-controlling final target torque for controlling the fuelinjector 20.

Subsequently, in step S33, the engine control part 69 operates todetermine whether or not the combustion mode of the engine E in the lastcombustion cycle is a diffusion combustion mode.

As a result, when the combustion mode of the engine E in the lastcombustion cycle is the diffusion combustion mode, the subroutineproceeds to step S34. In the step S34, the engine control part 69operates to determine whether or not the engine operation state(specifically, the fuel injection-controlling final target torque andthe engine speed of the engine E) in a current combustion cycle isincluded in a premixed combustion region.

Here, with reference to FIG. 7, a relationship between the engineoperation state and the combustion mode will be described. In acombustion mode map in FIG. 7, the horizontal axis represents the enginespeed, and the vertical axis represents the engine load (in thisembodiment, the fuel injection-controlling final target torque). Asdepicted in FIG. 7, the premixed combustion region A is set in a rangewhere the engine speed and the engine load are relatively low, and twodiffusion combustion regions B, C are set in a range except the premixedcombustion region.

That is, in the step S34, the engine control part 69 operates todetermine whether or not the operation state of the engine E in thecurrent combustion cycle is included in the low engine speed and lowengine load, premixed combustion region (the region A in FIG. 7). As aresult, when the operation state of the engine E in the currentcombustion cycle is included in the premixed combustion region, thesubroutine proceeds to step S35. In the step S35, the engine controlpart 69 operates to maintain the last combustion mode (i.e., diffusioncombustion mode) to serve as the current combustion mode, irrespectiveof the operation state of the engine E in the current combustion cycle.

Referring to the step S31 again, when there is no need for the torquereduction based on the vehicle driving state other than the manipulationof the accelerator pedal, the subroutine proceeds to step S36. In thestep S36, the final target torque-determining part 65 operates todetermine the basic target torque after being smoothed in the step S4,as the fuel injection-controlling final target torque.

Subsequently, in step S37, the engine control part 69 operates to set acombustion mode corresponding to the operation state of the engine E inthe current combustion cycle, based on the combustion mode mapexemplified in FIG. 7. Specifically, the engine control part 69 operatesto set the combustion mode in the current combustion cycle to a premixedcombustion mode, when the operation state of the engine E in the currentcombustion cycle is included in the premixed combustion region A, andset the combustion mode in the current combustion cycle to the diffusioncombustion mode, when the operation state of the engine E in the currentcombustion cycle is included in the diffusion combustion region B or C.

Referring to the step S33 again, when the combustion mode of the engineE in the last combustion cycle is not the diffusion combustion mode (isthe premixed combustion mode), the subroutine proceeds to the step S37.In the step S37, the engine control part 69 operates to set thecombustion mode corresponding to the operation state of the engine E inthe current combustion cycle, based on the combustion mode mapexemplified in FIG. 7.

For example, when the combustion mode of the engine E in the lastcombustion cycle is the premixed combustion mode, and the operationstate of the engine E in the current combustion cycle is included in thediffusion combustion region B or C, the engine control part 69 operatesto switch the current combustion mode from the premixed combustion modewhich is the last combustion mode, to the diffusion combustion mode.

Referring to the step S34 again, when the operation state of the engineE in the current combustion cycle is not included in the premixedcombustion region (is included in the diffusion combustion region), thesubroutine proceeds to the step S37. In the step S37, the engine controlpart 69 operates to set the combustion mode corresponding to theoperation state of the engine E in the current combustion cycle, basedon the combustion mode map exemplified in FIG. 7. Specifically, theengine control part 69 operates to set the combustion mode in thecurrent combustion cycle to the diffusion combustion mode.

After completion of the processing in the step S35 or S37, the PCM 60operates to terminate the combustion mode setting processing subroutine,and the subroutine returns to the main routine.

Returning to FIG. 3 again, after completion of the combustion modesetting processing subroutine in the step S6, in step S7, the enginecontrol part 69 operates to set a basic fuel injection parameter forcontrolling the fuel injector 20. Examples of the basic fuel injectionparameter include a required fuel injection amount, and the number oftimes of fuel injection, a fuel injection timing in each injection and afuel injection amount in each injection, in the case of performingmultistage fuel injection. The basic fuel injection parameter ispreliminarily set in association with the engine operation state.

For example, as depicted in FIG. 7, in the premixed combustion region A,the basic fuel injection parameter is set such that a main injectiondivided into three partial injections is performed beforetop-dead-center of compression stroke. On the other hand, in thediffusion combustion region B which is one of the two diffusioncombustion regions where the engine load is relatively low, the basicfuel injection parameter is set such that two pre-stage injections(pilot injection(s) and/or pre-injection(s)) and one main injection areperformed before and after top-dead-center of compression stroke. In thediffusion combustion region C which is the other diffusion combustionregion where the engine load is relatively high, the basic fuelinjection parameter is set such that one pre-stage injection and onemain injection are performed before and after top-dead-center ofcompression stroke.

Subsequently, in step S8, the engine control part 69 operates to obtaina fuel injection parameter correction value for correcting the basicfuel injection parameter set in the step S7.

Specifically, when the combustion mode of the engine E is the diffusioncombustion mode, the engine control part 69 operates to obtain a fuelinjection parameter correction value for reducing the fuel injectionamount in the pre-stage injection(s), upon a change in the fuelinjection-controlling final target torque corresponding to a change inthe torque reduction amount.

On the other hand, when the combustion mode of the engine E is thepremixed combustion mode, the engine control part 69 operates to obtaina fuel injection parameter correction value for retarding the fuelinjection timing in the main injection, upon a change in the fuelinjection-controlling final target torque corresponding to a change inthe torque reduction amount.

These fuel injection parameter correction values are set based on adifference between an oxygen concentration in a cylinder of the engine E(in-cylinder oxygen concentration), and a target in-cylinder oxygenconcentration necessary for enabling the engine E to output the fuelinjection-controlling final target torque. In this embodiment, theengine control part 69 operates to estimate the in-cylinder oxygenconcentration by an intake and exhaust model in which an oxygenconcentration of gas in intake and exhaust paths is modeled, usingparameters such as intake charge amount, an intake air amount, and aflow rate and an oxygen concentration of EGR gas. In this case, theintake charge amount is calculated based on detection signals from theintake air pressure sensor 108 and an intake manifold temperaturesensor. The intake air amount is specified by the detection sensor S101from the airflow sensor 101. Further, the oxygen concentration of EGRgas is calculated based on detection signals S110 from the linear O₂sensor 110, and a time lag before the linear O₂ sensor 110 can actuallydetect an oxygen concentration of exhaust gas.

Here, with reference to FIG. 8, a relationship of a difference betweenan estimated in-cylinder oxygen concentration and a target in-cylinderoxygen concentration, and the fuel injection parameter correction value.Chart (a) is a correction map to be used when the combustion mode of theengine E is the premixed combustion mode, and chart (b) is a correctionmap to be used when the combustion mode of the engine E is the diffusioncombustion mode. In these correction maps, the horizontal axisrepresents a difference value obtained by subtracting the targetin-cylinder oxygen concentration from the estimated in-cylinder oxygenconcentration, and the vertical axis represents the fuel injectionparameter correction value.

When the combustion mode of the engine E is the premixed combustionmode, a correction value of the fuel injection timing in the maininjection is set such that it becomes larger toward a retard side, alongwith an increase in the difference between the estimated in-cylinderoxygen concentration and the target in-cylinder oxygen concentration, aspresented in chart (a).

On the other hand, when the combustion mode of the engine E is thediffusion combustion mode, a correction value of the fuel injectionamount in the pre-stage injection(s) is set such that it becomes largertoward a reduction side, along with an increase in the differencebetween the estimated in-cylinder oxygen concentration and the targetin-cylinder oxygen concentration, as presented in chart (b).

Returning to FIG. 3 again, in step S9, the engine control part 69operates to correct the basic fuel injection parameter set in the stepS7 by the fuel injection parameter correction value obtained in the stepS8. Specifically, when the combustion mode of the engine E is thepremixed combustion mode, the engine control part 69 operates togradually retard the fuel injection timing of the main injection alongwith an increase in the difference between the estimated in-cylinderoxygen concentration and the target in-cylinder oxygen concentration. Onthe other hand, when the combustion mode of the engine E is thediffusion combustion mode, the engine control part 69 operates togradually reduce the fuel injection amount in the pre-stage injection(s)along with an increase in the difference between the estimatedin-cylinder oxygen concentration and the target in-cylinder oxygenconcentration.

Then, in step S10, the engine control part 69 operates to control thefuel injector 20 based on a fuel injection parameter corrected in thestep S9

In parallel with the processings in the steps S7 to S10, in step S11,the final target torque-determining part 65 operates to determine thebasic target torque after being smoothed in the step S4, as an EGR andturbocharger-controlling final target torque for controlling theturbocharger 5 and the EGR device 43.

Subsequently, in step S12, the engine control part 69 operates to set,based on the EGR and turbocharger-controlling final target torque set inthe step S11, and the engine speed, a required fuel injection amount tobe injected from the fuel injector 20 so as to enable the engine E tooutput the EGR and turbocharger-controlling final target torque.

Subsequently, in step S13, the engine control part 69 operates to setthe target in-cylinder oxygen concentration, a target intake airtemperature, and an EGR control mode (control mode for activating theEGR device 43, or control mode for deactivating the EGR device 43),based on the required fuel injection amount set in the step S12, and theengine speed.

Subsequently, in step S14, the engine control part 69 operates to setvarious state quantities for realizing the target in-cylinder oxygenconcentration and the target intake air temperature set in the step S13.Examples of the state quantities include an amount of exhaust gas to berecirculated to the intake system IN by the EGR device 43 (EGR gasamount), and a supercharging pressure by the turbocharger 5.

Subsequently, in step S15, the engine control part 69 operates tocontrol respective actuators for driving the components of the enginesystem 200, based on the state quantities set in the step S14.

In this embodiment, the engine control part 69 operates tofeedforward-control the EGR device 43 to realize the state quantitiesset in the step S14, and feedback-control the EGR device 43 to causeactual in-cylinder state quantities (in-cylinder oxygen concentrationand intake air temperature) to come close to the state quantities (i.e.,the target in-cylinder oxygen concentration and the target intake airtemperature) set in the step S13

Before performing the control, the engine control part 69 operates toset a limit value or range with respect to each of the state quantities,and set a control amount of each of the actuator to enable its relatedstate value to preserve limitation by the limit value or range.

After completion of the steps S10 and S15, the PCM 60 operates toterminate the engine control processing routine.

Next, with reference to FIG. 9, an operation of the engine controldevice according to this embodiment will be described. FIG. 9 presents atemporal change in each parameter regarding engine control to beperformed by the engine control device according to this embodimentduring turning of a vehicle equipped with the engine control device.

Chart (a) is a top plan view schematically depicting the vehicle whichis turning in a clockwise direction. As depicted in chart (a), thevehicle starts to turn from a position A, and continues to turn from aposition B to a position C in the clockwise direction at a constantsteering angle.

Chart (b) is a time chart presenting a change in the steering angle ofthe vehicle which is turning in the clockwise direction as depicted inchart (a). In chart (b), the horizontal axis represents time, and thevertical axis represents the steering angle.

As presented in chart (b), clockwise steering is started at the positionA, and then, along with additional turning manipulation of the steeringwheel, a clockwise steering angle gradually increases and reaches amaximum value at the position B. Subsequently, the steering angle ismaintained constant until the vehicle reaches the position C (Keeping ofthe steering angle).

Chart (c) is a time chart presenting a change in the steering speed ofthe vehicle which is turning in the clockwise direction as depicted inchart (a). In chart (c), the horizontal axis represents time, and thevertical axis represents the steering speed.

The steering speed of the vehicle is expressed as a temporaldifferentiation of the steering angle of the vehicle. That is, aspresented in chart (c), when clockwise steering is started at theposition A, a clockwise steering speed arises and is maintainedapproximately constant in an intermediate zone between the position Aand the position B. Then, when the clockwise steering speed decreases,and the clockwise steering angle reaches the maximum value at theposition B, the steering speed becomes 0. Then, when the clockwisesteering angle is maintained during traveling from the position B to theposition C, the steering speed is kept at 0.

Chart (d) is a time chart presenting a change in the additionaldeceleration determined based on the steering speed presented in chart(c). In chart (d), the horizontal axis represents time, and the verticalaxis represents the additional deceleration. In chart (d), the solidline indicates a change in the additional deceleration determined in thetorque reduction amount determination processing subroutine in FIG. 4,and the one-dot chain line indicates a change in the target additionaldeceleration based on the steering speed. As with the change in thesteering speed presented in chart (c), the target additionaldeceleration indicated by the one-dot chain line starts to increase fromthe position A, and is maintained approximately constant in theintermediate zone between the position A and the position B, whereafterit decreases and becomes 0 at the position B.

As described with reference to FIG. 4, when the absolute value of thesteering speed is determined in the step S23 to be not decreasing, i.e.,to be increasing or to have no change, the torque reductionamount-determining part 63 operates in the step S24 to obtain the targetadditional deceleration based on the steering speed. Subsequently, inthe step S25, the torque reduction amount-determining part 63 operatesto determine an additional deceleration in each processing cycle, underthe condition that the increase rate of the additional deceleration isequal to or less than the threshold R_(max).

Chart (d) presents an example in which the increase rate of the targetadditional deceleration starting to increase from the position A isgreater than the threshold R_(max). In this case, the torque reductionamount-determining part 63 operates to increase the additionaldeceleration at an increase rate equal to the upper limit R_(max) (i.e.,at an increase rate providing a gentler slope than that of the targetadditional deceleration indicated by the one-dot chain line). Then, whenthe target additional deceleration is maintained approximately constantin the intermediate zone between the position A and the position B, thetorque reduction amount-determining part 63 operates to determine theadditional deceleration such that it becomes equal to the targetadditional deceleration.

Then, when the absolute value of the steering speed is determined in thestep S23 depicted in FIG. 4 to be decreasing, the torque reductionamount-determining part 63 operates to maintain the additionaldeceleration at the maximum steering speed, as mentioned above.Specifically, in chart (d), when the steering speed decreases toward theposition B, the target additional deceleration indicated by the one-dotchain line also decreases along therewith, but the additionaldeceleration indicated by the solid line is maintained at its maximumvalue, until the vehicle reaches the position B.

On the other hand, when the absolute value of the steering angle isdetermined, in the step S21 depicted in FIG. 4, to be maintainedconstant or to be decreasing, the torque reduction amount-determiningpart 63 operates to obtain the deceleration reduction amount in the stepS27, and reduce the additional deceleration by the obtained decelerationreduction amount, as mentioned above. In chart (d), the torque reductionamount-determining part 63 operates to reduce the additionaldeceleration to cause a reduction rate of the additional deceleration tobecome gradually smaller, i.e., to cause a slope of the solid lineindicative of a change in the additional deceleration to becomegradually gentler.

Chart (e) is a time chart presenting a change in the torque reductionamount determined based on the additional deceleration presented inchart (d). In chart (e), the horizontal axis represents time, and thevertical axis represents the torque reduction amount.

As mentioned above, the torque reduction amount-determining part 63operates to determine a value of the torque reduction amount requiredfor realizing the current-cycle additional deceleration, based onparameters such as current vehicle speed, transmission gear stage androad grade. Thus, in the case where respective values of theseparameters are constant, the torque reduction amount is determined suchthat it changes in the same pattern as that of the additionaldeceleration presented in chart (d).

Chart (f) is a time chart presenting changes in the basic target torquebefore and after being smoothed by the torque variation filter 67. Inchart (f), the horizontal axis represents time, and the vertical axisrepresents torque. Further, in chart (f), the dotted line indicates thebasic target torque before being smoothed by the torque variation filter67, and the solid line indicates the basic target torque after beingsmoothed by the torque variation filter 67.

The basic target torque determined so as to realize the targetacceleration set based on current accelerator position, vehicle speed,transmission gear stage and others is likely to have a steep variationdue to various disturbances or noises, as indicated by the dotted linein chart (f). By subjecting this basic target torque to smoothing usingthe torque variation filter 67, the steep variation is suppressed asindicated by the solid line in chart (f), and thus rapid accelerationand deceleration of the vehicle is suppressed.

Chart (g) is a time chart presenting a change in the fuelinjection-controlling final target torque determined based on the basictarget torque and the torque reduction amount. In chart (g), thehorizontal axis represents time, and the vertical axis representstorque. Further, in chart (g), the dotted line indicates the smoothedbasic target torque presented in chart (f), and the solid line indicatesthe fuel injection-controlling final target torque.

As described with reference to FIG. 3, the final targettorque-determining part 65 operates to subtract the torque reductionamount determined by the torque reduction amount determinationprocessing subroutine in the step S5, from the basic target torque afterbeing smoothed in the step S4, to thereby determine the fuelinjection-controlling final target torque. In the basic target torqueand the torque reduction amount to be used for determining the finaltarget torque, only the basic target torque determined based on thevehicle driving state including the manipulation of the acceleratorpedal is subjected to smoothing using the torque variation filter 67. Inother words, in regard to a part of a temporal variation of the finaltarget torque corresponding to the torque reduction amount determinedbased on the manipulation of the steering wheel as the vehicle drivingstate other than the manipulation of the accelerator pedal, the torquereduction amount is not subjected to smoothing using the torquevariation filter 67. Thus, as indicated by the solid line in chart (g),the torque reduction amount is directly reflected on the final targettorque without being smoothed by the torque variation filter 67.

Due to such a change in the fuel injection-controlling final targettorque corresponding to a change in the torque reduction amount, whenthe operation state of the engine E changes from the diffusioncombustion region to the premixed combustion region, the engine controlpart 69 operates to maintain the combustion mode of the engine E in thediffusion combustion mode, as described in connection with the step S35in FIG. 6. On the other hand, due to the above change in the fuelinjection-controlling final target torque corresponding to a change inthe torque reduction amount, when the operation state of the engine Echanges from the premixed combustion region to the diffusion combustionregion, the engine control part 69 operates to switch the combustionmode of the engine E from the premixed combustion mode to the diffusioncombustion mode, as described in connection with the steps S33 and S37in FIG. 6.

Chart (h) is a time chart presenting a change in the EGR andturbocharger-controlling final target torque determined based on thebasic target torque. In chart (h), the horizontal axis represents time,and the vertical axis represents torque.

As described with reference to FIG. 3, the final targettorque-determining part 65 operates to determine the basic target torqueafter being smoothed in the step S4, as the EGR andturbocharger-controlling final target torque for controlling theturbocharger 5 and the EGR device 43. Thus, as presented in chart (h),the EGR and turbocharger-controlling final target torque temporallychanges in the same pattern as that of the temporal change in thesmoothed basic target torque.

Chart (i) is a time chart presenting a change in the required fuelinjection amount determined based on the fuel injection-controllingfinal target torque. In chart (i), the horizontal axis represents time,and the vertical axis represents the required fuel injection amount.Further, in chart (i), the dotted line indicates the required fuelinjection amount corresponding to the smoothed basic target torquepresented in chart (f), and the solid line indicates the required fuelinjection amount corresponding to the fuel injection-controlling finaltarget torque presented in chart (g).

In the example in chart (i), the engine control part 69 operates tocontrol, by a fuel injection amount to be injected from the fuelinjector 20, a part of a temporal variation of the fuelinjection-controlling final target torque set in the step S6,corresponding to the torque reduction amount. Thus, as indicated by thesolid line in chart (i), the required fuel injection amount temporallychanges in the same pattern as that of the fuel injection-controllingfinal target torque presented in chart (g).

Chart (j) is a time chart representing the target in-cylinder oxygenconcentration and an actual in-cylinder oxygen concentration, in thecase where the fuel injection amount is controlled as presented in chart(i). In chart (j), the horizontal axis represents time, and the verticalaxis represents the in-cylinder oxygen concentration. Further, in chart(j), the dotted line indicates the target in-cylinder oxygenconcentration determined based on the EGR and turbocharger-controllingfinal target torque presented in chart (h), and the solid line indicatesthe actual in-cylinder oxygen concentration (i.e., the in-cylinderoxygen concentration estimated by the engine control part 69).

Chart (k) is a time chart presenting a change in the difference betweenthe actual in-cylinder oxygen concentration and the target in-cylinderoxygen concentration. In chart (k), the horizontal axis represents time,and the vertical axis represents the difference between the actualin-cylinder oxygen concentration and the target in-cylinder oxygenconcentration.

When the fuel injection amount is controlled to realize the fuelinjection-controlling final target torque, as indicated by the solidline in chart (i), the in-cylinder oxygen concentration will changeaccording to this fuel injection amount. That is, when the fuelinjection amount starts to decrease according to a decrease in the fuelinjection-controlling final target torque corresponding to the torquereduction amount, an amount of oxygen consumed by combustion decreases.Thus, as indicated in the solid line in chart (j), the in-cylinderoxygen concentration starts to increase at timing T1 delayed from startof the decrease in the fuel injection amount. After that, when the fuelinjection amount increases correspondingly to an increase in the fuelinjection-controlling final target torque, the amount of oxygen consumedby combustion increases. Thus, the in-cylinder oxygen concentrationstarts to decrease at timing T2 delayed from start of the increase inthe fuel injection amount.

On the other hand, a change in the torque reduction amount is notreflected on the EGR and turbocharger-controlling final target torque,and thus the EGR and turbocharger-controlling final target torquetemporally changes in the same pattern as that a temporal change in thesmoothed basic target torque, as presented in chart (h), so that thetarget in-cylinder oxygen concentration set based on the EGR andturbocharger-controlling final target torque temporally changes in thesame pattern as that the temporal change in the smoothed basic targettorque without changing according to the torque reduction amount, asindicated by the dotted line in chart (j).

Assume a situation where the fuel injection-controlling final targettorque decreases as indicated by the solid line in chart (g), and thusthe operation state of the engine E changes from the diffusioncombustion region to the premixed combustion region. In this situation,if the combustion mode of the engine E is changed from the diffusioncombustion mode to the premixed combustion mode, the in-cylinder oxygenconcentration needs to be reduced, as compared to during the diffusioncombustion mode. However, the in-cylinder oxygen concentration ratherrises according to the decrease in the fuel injection-controlling finaltarget torque, as indicated by the solid line in chart (j), so that adifference between the actual in-cylinder oxygen concentration and atarget in-cylinder oxygen concentration suitable for the premixedcombustion mode is increased, thereby leading to occurrence of abnormalcombustion such as premature ignition. Therefore, when the operationstate of the engine E changes from the diffusion combustion region tothe premixed combustion region, the engine control part 69 operates tomaintain the combustion mode of the engine E in the diffusion combustionmode, so that it is possible to avoid the need to reduce the in-cylinderoxygen, and thus suppress an increase in the difference between theactual in-cylinder oxygen concentration and the target in-cylinderoxygen concentration.

On the other hand, when, due to a decrease in the fuelinjection-controlling final target torque, the operation state of theengine E changes from the premixed combustion region to the diffusioncombustion region, and the combustion mode of the engine E is changedfrom the premixed combustion mode to the diffusion combustion mode, thein-cylinder oxygen concentration needs to be raised, as compared toduring the diffusion combustion mode. Specifically, as indicated by thesolid line in chart (j), the in-cylinder oxygen concentration risesaccording to a decrease in the fuel injection-controlling final targettorque, and the target in-cylinder oxygen concentration also rises inresponse to the switching of the combustion mode from the premixedcombustion mode to the diffusion combustion mode, so that it is possibleto suppress an increase in a difference between the actual in-cylinderoxygen concentration and a target in-cylinder oxygen concentrationsuitable for the diffusion combustion mode.

Therefore, the engine control part 69 is capable of, when the operationstate of the engine E changes from the premixed combustion region to thediffusion combustion region, switching the combustion mode of the engineE from the premixed combustion mode to the diffusion combustion mode,i.e., setting a suitable combustion mode for the operation state of theengine E, as mentioned above.

Further, when the combustion mode of the engine E is the premixedcombustion mode, the engine control part 69 operates to gradually retardthe fuel injection timing of the main injection as the differencebetween the actual in-cylinder oxygen concentration and the targetin-cylinder oxygen concentration becomes larger as presented in chart(k), according to a decrease in the fuel injection-controlling finaltarget torque. As a result, the center of gravity of combustion isretarded. Thus, even in a situation where the difference between theactual in-cylinder oxygen concentration and the target in-cylinderoxygen concentration increases, it becomes possible to suppress a rapidrise in in-cylinder pressure around top-dead-center of compressionstroke to thereby suppress occurrence of abnormal combustion or knocknoise.

On the other hand, when the combustion mode of the engine E is thediffusion combustion mode, the engine control part 69 operates togradually reduce the fuel injection amount in the pre-stage injection(s)along with an increase in the difference between the estimated actualin-cylinder oxygen concentration and the target in-cylinder oxygenconcentration. As a result, enhancement in ignitability by the pre-stageinjection(s) is suppressed. Thus, even in the situation where thedifference between the actual in-cylinder oxygen concentration and thetarget in-cylinder oxygen concentration increases, it becomes possibleto suppress a rapid combustion during the main combustion to therebysuppress generation of knock noise.

Chart (1) is a time chart presenting a change in yaw rate (actual yawrate) generated in the vehicle being steered as presented in chart (b),when the fuel injection amount is controlled based on the fuelinjection-controlling final target torque presented in chart (i), and achange in actual yaw rate generated in the vehicle when controlcorresponding to the torque reduction amount presented in chart (e) isnot performed (i.e., control of the fuel injection amount is performedbased on the smoothed basic target torque indicated by the dotted linein chart (g)). In chart (1), the horizontal axis represents time, andthe vertical axis represents yaw rate. Further, in chart (1), the solidline indicates a change in the actual yaw rate when the control of thefuel injection amount is performed based on the fuelinjection-controlling final target torque, and the dotted line indicatesa change in the actual yaw rate when the control corresponding to thetorque reduction amount is not performed.

After clockwise steering is started at the position A, when the torquereduction amount is increased as presented in chart (e) along with anincrease in clockwise steering speed, a load applied to the front roadwheels as steerable road wheels of the vehicle is increased. As aresult, a frictional force between each of the front road wheels and aroad surface is increased, and a cornering force of the front roadwheels is increased, thereby providing an improved turn-in ability ofthe vehicle. That is, as depicted in chart (l), in the intermediate zonebetween the position A and the position B, when the control of the fuelinjection amount is performed based on the fuel injection-controllingfinal target torque reflecting the torque reduction amount (solid line),a larger clockwise (CW) yaw rate is generated in the vehicle, ascompared to the case where the control corresponding to the torquereduction amount is not performed (dotted line).

In addition, as depicted in charts (d) and (e), when the steering speedis gradually reduced toward the position B, the torque reduction amountis maintained at its maximum value, although the target additionaldeceleration is reduced, so that it is possible to maintain the loadapplied to the front road wheels and keep up the turn-in ability of thevehicle, as long as the tuning of the steering wheel is continued.

Further, when the absolute value of the steering angle is maintainedconstant during traveling from the position B to the position C, thetorque reduction amount is smoothly reduced. Thus, in response tocompletion of the turning of the steering wheel, the load applied to thefront road wheels can be gradually reduced to gradually reduce thecornering force of the front road wheels, thereby restoring the outputtorque of the engine E, while stabilizing a vehicle body.

Next, some modifications of the above embodiment will be described.

Although the above embodiment has been described based on an example inwhich the torque reduction amount-determining part 63 is configured toobtain the target additional deceleration based on the steering speed,and determine the torque reduction amount based on the obtained targetadditional deceleration, the torque reduction amount-determining part 63may be configured to determine the torque reduction amount based on anydriving state of the vehicle other than the manipulation of theaccelerator pedal (e.g., steering angle, yaw rate, or slip ratio).

For example, the torque reduction amount-determining part 63 may beconfigured to calculate a target yaw acceleration to be generated in thevehicle, based on a target yaw rate calculated from the steering angleand the vehicle speed, and a yaw rate input from a yaw rate sensor, andobtain the target additional deceleration based on the calculated targetyaw acceleration to determine the torque reduction amount.Alternatively, a lateral acceleration generated along with turning ofthe vehicle may be detected by an acceleration sensor, and the torquereduction amount may be determined based on the determined lateralacceleration. Alternatively, the torque reduction amount-determiningpart 63 may be configured to determine the torque reduction amount,based on any demand different from the target additional deceleration(e.g., a torque required for cancelling out vibration of a powertrainduring acceleration/deceleration).

Although the above embodiment has been described based on an example inwhich the engine control part 69 is configured to control theturbocharger 5 based on the EGR and turbocharger-controlling finaltarget torque which does not reflect the torque reduction amount (i.e.,based on the smoothed basic target torque), the engine control part 69may be configured to control the turbocharger 5 based on an EGR andturbocharger-controlling final target torque reflecting the torquereduction amount. In this case, the engine control part 69 is configuredto restrict controlling the turbocharger 5 according to a change in thefinal target torque corresponding to a change in the torque reductionamount. For example, the final target torque-determining part 65 may beconfigured to, in the step S10 of the engine control processing routinedepicted in FIG. 3, multiply the torque reduction amount determined inthe torque reduction amount determination processing subroutine in thestep S5 by a correction coefficient of less than 1 to obtain a correctedtorque reduction amount, and then subtract the corrected torquereduction amount from the basic target torque after being smoothed inthe step S4, to thereby determine an EGR and turbocharger-controllingfinal target torque for controlling the turbocharger 5 and the EGRdevice 43. In the EGR and turbocharger-controlling final target torquedetermined in this manner, a change in the final target torquecorresponding to a change in the torque reduction amount is reduced, ascompared to the fuel injection-controlling final target torque obtainedby directly subtracting the torque reduction amount from the basictarget torque, so that it is restricted to control the turbocharger 5according to a change in the final target torque corresponding to achange in the torque reduction amount.

Although the above embodiment has been described based on an example inwhich the turbocharger 5 is constructed as the two-stage superchargingsystem comprising the large turbocharger 5 a and the small turbocharger5 b, the turbocharger 5 may be constructed as a variable geometryturbocharger (VGT) comprising a plurality of movable flaps provided tosurround the entire circumference of a turbine, wherein across-sectional flow area (cross-sectional nozzle area) with respect tothe turbine can be changed by the movable flaps. In this case, theengine control part 69 may be configured to control an opening degree ofthe flaps, based on the target supercharging pressure.

Next, advantageous effects of the engine control device according toeach of the above embodiment and the modifications of the embodimentwill be described.

First of all, the engine control part 69 is configured to control theengine E to output the fuel injection-controlling final target torquereflecting the torque reduction amount determined based on the vehicledriving state other than the manipulation of the acceleration pedal, sothat it is possible to control the engine to obtain the torque reductionamount with high responsivity with respect to the vehicle driving stateother than the manipulation of the accelerator pedal, to thereby quicklyapply a load to front road wheels. This makes it possible to control theengine to accurately realize vehicle behavior intended by a driver.

Further, the engine control part 69 is configured, when the operationstate of the engine E changes from the diffusion combustion region tothe premixed combustion region, due to a change in the final targettorque corresponding to a change in the torque reduction amount, tomaintain the combustion mode of the engine E in the diffusion combustionmode, so that it is possible to avoid the need to reduce the in-cylinderoxygen concentration in response to switching of the combustion modefrom the diffusion combustion mode to the premixed combustion mode, andthus suppress an increase in the difference between the actualin-cylinder oxygen concentration and the target in-cylinder oxygenconcentration for the combustion mode. This makes it possible tosuppress generation of knock noise due to abnormal combustion such aspremature ignition.

In particular, the torque reduction amount-determining part 63 isconfigured to determine the torque reduction amount according to themanipulation of the steering wheel of the vehicle. Thus, a temporalchange in the torque reduction amount determined based on themanipulation of the steering wheel can be reflected on a temporal changein the final target torque, so that it is possible to quickly add, tothe vehicle, deceleration according to the manipulation of the steeringwheel by a driver to thereby apply a load to front road wheels toquickly increase a cornering force, thereby improving responsivity withrespect to the manipulation of the steering wheel. This makes itpossible to control the engine to accurately realize vehicle behaviorintended by the driver, while suppressing generation of knock noise dueto abnormal combustion such as premature ignition.

Further, the engine control part 69 is configured, when the operationstate of the engine E changes from the premixed combustion region to thediffusion combustion region, due to a change in the final target torquecorresponding to a change in the torque reduction amount, to switch thecombustion mode of the engine E from the premixed combustion mode to thediffusion combustion mode. Thus, when the actual in-cylinder oxygenconcentration rises according to a reduction in the fuelinjection-controlling final target torque corresponding to a change inthe torque reduction amount, the target in-cylinder oxygen concentrationalso rises in response to the switching of the combustion mode from thepremixed combustion mode to the diffusion combustion mode, so that it ispossible to suppress an increase in the difference between the actualin-cylinder oxygen concentration and the suitable in-cylinder oxygenconcentration for the combustion mode, and thus appropriately set thecombustion mode according to the operation state of the engine E, whilesuppressing generation of knock noise due to abnormal combustion such aspremature ignition. This makes it possible to achieve enhancedcombustion stability and improved emission quality.

Further, in the engine control device, the engine is a diesel enginecomprising a fuel injector 20 for injecting fuel into a cylinder. Thus,the engine control device is capable of changing the fuel injectionamount in the diesel engine, according to the fuel injection-controllingfinal target torque reflecting the torque reduction amount to therebyaccurately realize a temporal change in the torque reduction amountdetermined based on the vehicle driving state other than the acceleratorpedal, with high responsivity. This makes it possible to control thediesel engine so as to accurately realize vehicle behavior intended by adriver.

Further, the engine control part 69 is configured, when the fuelinjection-controlling final target torque changes correspondingly to achange in the torque reduction amount, to correct the fuel injectionparameter preliminarily set in association with the operation state ofthe engine E. Thus, even in a situation where a mismatch occurs betweenthe target in-cylinder oxygen concentration and the actual in-cylinderoxygen concentration, due to a change in the fuel injection-controllingfinal target torque, the fuel injection parameter can be corrected tosuppress a rapid rise in in-cylinder pressure and rapid combustion whichwould otherwise be caused by the mismatch, to thereby suppressgeneration of knock noise due to abnormal combustion such as prematureignition.

Further, when the combustion mode of the engine E is the diffusioncombustion mode, the engine control part 69 is configured to reduce thefuel injection amount in the pre-stage injection(s), upon a change inthe fuel injection-controlling final target torque corresponding to achange in the torque reduction amount. Thus, even in the situation wherea mismatch occurs between the target in-cylinder oxygen concentrationand the actual in-cylinder oxygen concentration, due to a change in thefuel injection-controlling final target torque, enhancement inignitability by the pre-stage injection(s) can be suppressed to suppressrapid combustion during the main injection to thereby reliably suppressgeneration of knock noise.

Further, when the combustion mode of the engine E is the premixedcombustion mode, the engine control part 69 is configured to retard thefuel injection timing of the main injection, upon a change in the fuelinjection-controlling final target torque corresponding to a change inthe torque reduction amount. Thus, even in the situation where amismatch occurs between the target in-cylinder oxygen concentration andthe actual in-cylinder oxygen concentration, due to a change in the fuelinjection-controlling final target torque, the center of gravity ofcombustion can be retarded to suppress a rapid rise in in-cylinderpressure around top-dead-center of combustion stroke to thereby reliablysuppress generation of knock noise.

Further, the engine control part 69 is configured, when the fuelinjection-controlling final target torque changes correspondingly to achange in the torque reduction amount, to gradually increase the fuelinjection parameter correction value along with an increase in thedifference between the actual in-cylinder oxygen concentration and thetarget in-cylinder oxide concentration. Thus, even in a situation wherethe mismatch between the target in-cylinder oxygen concentration and theactual in-cylinder oxygen concentration is increased, the fuel injectionparameter correction value can be increased to suppress a rapid rise inin-cylinder pressure and rapid combustion which would otherwise becaused by the mismatch, to thereby reliably suppress generation of knocknoise due to abnormal combustion such as premature ignition.

LIST OF REFERENCE SIGNS

-   1: intake passage-   5: turbocharger-   5 a: large turbocharger-   5 b: small turbocharger-   5 c: compressor bypass valve-   5 d: regulator valve-   5 e: waste gate valve-   20: injector-   41: exhaust passage-   43: EGR device-   60: PCM-   61: basic target torque-determining part-   63: torque reduction amount-determining part-   65: final target torque-determining part-   67: torque variation filter-   69: engine control part-   200: engine system-   E: engine

What is claimed is:
 1. A control device for an engine whose combustionmode is switchable according to an engine operation state, comprising: abasic target torque-determining part configured to determine a basictarget torque based on a driving state of a vehicle includingmanipulation of an accelerator pedal; a torque reductionamount-determining part configured to determine a torque reductionamount based on a driving state of the vehicle other than themanipulation of the accelerator pedal; a final target torque-determiningpart configured to determine a final target torque based on the basictarget torque and the torque reduction amount; and an engine controlpart configured to control the engine to output the final target torque,wherein the engine control part is configured, when the engine operationstate is in a predetermined premixed combustion region, to set thecombustion mode of the engine to a premixed combustion mode andconfigured, when the engine operation state is in a predetermineddiffusion combustion region, to set the combustion mode of the engine toa diffusion combustion mode, and wherein the engine control part isconfigured, when the engine operation state changes from the diffusioncombustion region to the premixed combustion region, due to a change inthe final target torque corresponding to a change in the torquereduction amount, to maintain the combustion mode of the engine in thediffusion combustion mode.
 2. The control device as recited in claim 1,wherein the torque reduction amount-determining part is configured todetermine the torque reduction amount according to manipulation of asteering wheel of the vehicle.
 3. The control device as recited in claim1, wherein the engine control part is configured, when the engineoperation state changes from the premixed combustion region to thediffusion combustion region, due to a change in the final target torquecorresponding to a change in the torque reduction amount, to switch thecombustion mode of the engine from the premixed combustion mode to thediffusion combustion mode.
 4. The control device as recited in claim 1,wherein the engine is a diesel engine comprising a fuel injector forinjecting fuel into a cylinder, and wherein the engine control part isconfigured to control the fuel injector to regulate a fuel injectionamount so as to enable the diesel engine to output the final targettorque.